Electrical measurement of biological activity, and particularly non-invasive electrical measurement, is increasingly important in medical therapy, diagnostics, and research. For example, electrodes of various types may be used to record electrocardiograms (ECGs), electroencephalograms (EEG), electromyogram (EMG), galvanic skin reflex (GSR), electrooculogram (EOG), bioimpedance (BI), and others, including invasive or implantable measurements. Accurate and reliable electrical measurements from patients may require precise or consistent placement of the electrodes used for measurement on the patient's body, which may require that the user placing the electrodes have a great deal of training and experience. The consequences of placing the electrodes outside of the predetermined, conventional, or standard locations on the body may result in inaccurate results.
For example electrocardiography is used to examine and monitor the electrical activity of the heart. ECGs are increasingly valuable tools for treating patients at risk for heart disorders. Electrocardiograms (ECG) can be recorded or taken using multiple electrodes placed on the skin of a patient, and electrical signals recorded between two electrodes may be referred to as leads. A variety of different lead patterns, including different numbers of electrodes, may be used to take an ECG. For example, an ECG may be taken with 3, 5, and 12 leads. For a standard 12-lead ECG, 10 electrode positions are typically used: six on the chest, and one on each of the patient's arms and legs.
The placement of the electrodes for the ECG is important. Despite the common use of ECGs within the medical profession, it is not uncommon for electrodes to be incorrectly placed on the patient by the nurse, medical technician, or physician. Incorrect placement of electrodes can adversely affect the ECG results and make comparison of the ECG results to standard ECG data difficult. Because of this sensitivity, the placement of leads is typically left to trained medical technicians (e.g., ECG technicians), as it is difficult for an untrained user to correctly place electrodes; it would be particularly difficult for an untrained user to correctly place leads on their own body. As mentioned, placing one or more of the electrodes used to measure an ECG outside of the accepted (standard or conventional) positions on the patient's body can affect the ECG, making it difficult to compare to a standard ECG and therefore difficult for a medical professional to interpret.
Electrodes are typically placed on a patient by a human, allowing an opportunity for human error to result in incorrect electrode placement. The methods, devices and systems disclosed herein can be used to improve guide the electrode placement on a patient. Accurate electrode placement can result in improved patient data (e.g., ECG data), better patient diagnosis and treatment, and improved patient health. Although attempts have been made to minimize the error introduced by varying electrode placement in ECG systems, including creating systems that are supposed to tolerate a greater variability in ECG measurement, these efforts have had limited success. For example, U.S. Pat. No. 6,282,440 describes methods for calculating and determining whether electrodes are in the standard ECG electrode placement, an alternative electrode placement, or an incorrect electrode placement based on an analysis of the ECG measurements resulting from electrode placement. Unfortunately, U.S. Pat. No. 6,282,440 does not provide a method for guiding the initial placement of electrodes or easily correcting incorrect measurements.
Different configurations for ECG electrode placement may be used on a patient. Common, customary or standard positions for these ten electrode positions have been determined for use in taking a 12-lead ECG. Measurement taken from ten (10) electrode positions on a patient may be used to produce a standard 12-lead electrocardiogram (ECG).
Thus, a standard or conventional 12-lead ECG configuration typically uses 10 electrode positions, which may mean the placement of ten separate electrodes in these positions. FIG. 1 illustrates placement of 10 electrodes that may be used for a 12-lead ECG, with 6 electrodes on the patient's chest and one electrode on each of the patient's arms and legs. The electrode placed on the right arm is typically referred to as RA. The electrode placed on the left arm is referred to as LA. The RA and LA electrodes are placed at approximately the same location on the left and right arms, preferably near the wrist. The leg electrodes can be referred to as RL for the right leg and LL for the left leg. The RL and LL electrodes are placed on the same location for the left and right legs, preferably near the ankle. In practice placement of the arm and leg electrodes is much less challenging than placement of the electrodes on the patient's chest. Further, ECG measurements may be more sensitive to variations in the placement of chest electrodes.
FIG. 2 illustrates standard placement positions of the six electrode positions on the chest, labeled V1, V2, V3, V4, V5, and V6. For a standard 12-lead ECG measurement, V1 is typically placed in the fourth intercostal space, for example between ribs 4 and 5, just to the right of the sternum. V2 is placed in the fourth intercostal space, for example between ribs 4 and 5, just to the left of the sternum. V3 is placed between electrodes V2 and V4. V4 is placed in the fifth intercostal space between ribs 5 and 6 in the mid-clavicular line. V5 is placed horizontally even with V4 in the left anterior axillary line. V6 is placed horizontally even with V4 and V5 in the mid-axillary line. Electrodes are also typically positioned on the patient's right and left arm and right and left leg. This arrangement of electrode positions, including the positions on arms and legs, may be referred to as standard or conventional 12-lead ECG electrode positions.
Based on measurements between these electrode positions, standard “lead” measurements may be taken. For example, lead I is the voltage between the left arm (LA) and right arm (RA), e.g. I=LA−RA. Lead II is the voltage between the left leg (LL) and right arm (RA), e.g. II=LL−RA. Lead III is the voltage between the left leg (LL) and left arm (LA), e.g. III=LL−LA. Wilson's central terminal (WCT or Vw) can be calculated by (RA+LA+LL)/3. Augmented limb leads can also be determined from RA, RL, LL, and LA. The augmented vector right (aVR) is equal to RA−(LA+LL)/2 or −(I+II)/2. The augmented vector left (aVL) is equal to LA−(RA+LL)/2 or I−II/2. The augmented vector foot (aVF) is equal to LL−(RA+LA)/2 or II−I/2. Leads I, II, III, aVR, aVL, and aVF can all be represented on a hexaxial system illustrated in FIG. 3. Incorrect or shifted electrode placement can shift the results of the ECG on the hexaxial system.
The signals from this 12-lead system may be used to examine the electrical signal resulting from cardiac activity. The 12-lead measurements have been accepted as providing medically relevant information about cardiac health. FIG. 4 illustrates a sample ECG annotated to show characteristic features used for analysis of cardiac function, in particular PQRST waves. Identification and measurement of the PQRST waves across the 12 leads is well accepted as providing relevant information about the health of a patient. For example, FIG. 5 illustrates data collected from a patient using a 12-lead standard configuration. The data can be analyzed to obtain representations of the PQRST waves for this patient. As mentioned, incorrect placement of the electrodes changes the measured values for the leads.
There may be multiple acceptable positions (or ranges of positions) for electrodes, including ECG electrodes. For example, FIGS. 6A and 6B show different configurations for the arm and leg electrodes that may be used in an ECG. The RA/LA electrodes may be placed near the wrist, as shown in FIG. 6A, or near the shoulder, as shown in FIG. 6B, and the RL/LL electrodes may be placed near the ankle (FIG. 6A) or near the pelvis (FIG. 6B). Positioning the arm electrodes near the wrist and the leg electrodes near the ankles as shown in FIG. 6A is widely accepted as a standard or conventional electrode configuration for the arm and leg electrodes in a 12-lead ECG. Alternatively, positioning the arm and leg electrodes adjacent to the thorax as shown in FIG. 6B may be referred to as the Mason-Likar system for electrode placement. The Mason-Likar system is often used to take an ECG during exercise because the arm and leg electrodes are positioned closer to the chest and torso and placed in areas of the body that move less during exercise. The electrode positioning differences between the standard configuration and the Mason-Likar system can result in differences in the ECG signals received, since the relative positioning of the arm electrodes affects the measured leads (see, e.g., “Resting 12-Lead ECG Electrode Placement and Associated Problems” by Macfarlane et al., SCST Update 1995).
Thus, it would be beneficial to provide improved methods for accurately placing electrodes on the body of a patient.